1. Field of the Invention
This invention relates generally to systems for simulating wear conditions, and more particularly, to an arrangement and method of simulating friction environments, such as the friction conditions between components of an internal combustion engine.
2. Description of the Related Art
A significant portion of engine power within an internal combustion engine is lost as result of friction between the piston ring(s) and cylinder bore(s). There is need in the field of engine manufacture for a system that characterizes the frictional and wear characteristics of existing and new materials, so that their suitability for application within the various components of engines can be determined. Most commonly, gray iron is used as the cylinder bore material. This material is characterized as having good wear resistance due to hard carbide particles within it, but also a measure of lubricity is achieved by the graphite flakes contained therewithin which behave as a solid lubricant. Thus, the tribological properties of iron has resulted in cast iron liners being pressed or cast into aluminum engine blocks.
Aluminum alloys, thermal spray coated cylinder liners, and powder metal composites that contain solid lubricants have shown promising characteristics that may render these materials suitable as future cylinder bore material. However, extensive experimentation is required to understand the physical mechanisms of friction in cylinder liner-piston ring frictional contact.
Conventional friction and wear testing systems may include a pin on a disk, or block on a ring for testing. It is a problem with these known arrangements that they cannot simulate the operating conditions within an internal combustion engine. In fact, these known arrangements cannot produce reciprocating motion that would simulate the piston ring/cylinder wall interface in an internal combustion engine. The microstructure of a thermal spray coating that has been sprayed directly on to flat plates or rings is not representative of the microstructures obtained by spraying directly onto the cylinder gold liner surface. Thus, the use of actual engine components is highly desirable when simulating the friction environment in an engine, in order to maintain the actual geometry of the surface as well as its texture and microstructure.
It is a problem with known arrangements that test actual engines that they are expensive and their use is quite time consuming. Additionally, extensive modification of engine components is required. Gas and inertia forces are large compared to friction forces, and the temperature, load, and lubricant rate cannot be maintained constant during operation. It is additionally desired to distinguish the friction forces that result from the compression rings, from those that result from the oil ring, the piston skirt, and the bearings.
Current bench test systems have either very small stroke length and contact area, or low running speeds, which do not result in a close simulation of the actual engine conditions. There is, therefore, a need for an arrangement and a method of simulating frictional environments, that yield test results that are representative of the desired environment, such as the interior of an internal combustion engine, and which are repeatable to facilitate evaluation of advanced materials and lubricants.
The prior art has endeavored to produce wear testing systems that employ reciprocating motion. In one such system, an entire piston ring is positioned in a disk shaped holder, and the installed ring is reciprocated between static liner segments using a short stroke, on the order of one inch. This permits only small liner samples to be tested, two at a time. It is a problem with this known arrangement that its use limited to a short stroke at a relatively low running speed due to unbalanced inertia forces. It is a further problem that the disk-shaped holder that holds the complete piston ring is not representative of an actual piston. Still another problem with this known arrangement is that it is incapable of achieving simulation of various lubrication regimes.
It is, therefore, an object of this invention to provide a friction and wear simulation system that can be installed on a laboratory bench.
It is another object of this invention to provide a wear and friction simulation system that closely approximates a conditions encountered within an internal combustion engine.
It is also an object of the is invention to provide a friction and wear simulation system that can be operated at high speeds.
It is a further object of this invention to provide a wear and friction simulation system that allows a reciprocating stroke length corresponding to that of an actual internal combustion engine.
It is additionally an object of this invention to provide a wear and friction simulation system that enables testing at a plurality of lubricant delivery regimes.
The foregoing and other objects are achieved with this invention which provides, in a first apparatus aspect thereof, a system for simulating a friction environment between first and second wear elements in frictional communication with one another. In accordance with the invention, a first support arrangement supports the first wear element, and a reciprocating drive arrangement drives the first support arrangement reciprocatingly along the substantially axial path of reciprocation. A dynamic counterbalance arrangement is coupled to the reciprocating drive arrangement, and serves to nullify second order harmonic mechanical energy. A rotatory drive coupler is coupled to both, the reciprocating drive arrangement and the dynamic counterbalance arrangement. The rotatory drive coupler receives rotatory drive from a motor. A second support arrangement is provided for supporting the second wear element. A linear drive is coupled to the second support arrangement and urges same in the direction that is transverse to the substantially axial path of reciprocation. An electrical force signal responsive to a force applied by the linear drive to the second support arrangement is produced by a force gauge that is coupled to the linear drive.
In one embodiment of the invention, the second support arrangement is arranged to enable a transverse displacement of the second wear element with respect to the frictional communication with a first wear element. Thus, in embodiments of the invention where the second wear element is a portion of a piston ring, the ring portion is enabled to travel circumferentially for a limited distance within a groove that accommodates same within the second support arrangement. The second support arrangement may be, in certain embodiments, a portion of an actual piston of an internal combustion engine.
In another embodiment of the invention, the second support arrangement enables a transverse displacement of the second wear element with respect to the frictional communication with the first wear element. Again, in an embodiment of the invention where the second wear element is a portion of a piston ring on an internal combustion engine, the ring is permitted to tilt within the groove that accommodates same within the second support arrangement. Also, as stated, the second support arrangement in this embodiment of the invention may be a portion of a piston of an internal combustion engine.
In a further embodiment a rotational encoder produces and electrical signal that contains rotatory information relating to a rotational position of the rotatory drive coupling arrangement. In this manner, a signal is generated that permits instantaneous identification of the angular position of the rotatory drive coupler, and correspondingly, the first support arrangement. In an advantageous embodiment of the invention, the rotatory information contained within the electrical signal produced by the rotational encoder is correlated against the electrical force signal produced by the force gauge, whereby information in the form of a graphical representation can be provided corresponding to friction force as a function of angular displacement of the rotatory drive coupler. In a still further embodiment, a clock, which may be within a CPU, provides a time signal which, when correlated against, the rotatory information relating to the rotational position of the rotatory drive coupler produces instantaneous speed information.
In a practical embodiment of the invention, mechanical rotatory energy from the motor is delivered to the rotatory drive coupler by a power transfer belt. In a further embodiment, a rotatory inertial mass is coupled to the rotatory drive coupler to reduce angular speed variations. The rotatory inertial mass may be, in certain embodiments, a massive pulley that engages with the power transfer belt.
In a further embodiment, the first support arrangement includes a support bed for holding the first wear element, and a support guideway arrangement coupled to the support bed for constraining the support bed to travel along a substantially axial path of reciprocation. The support guideway includes, an elongated rail arranged parallel to the substantially axial path of reciprocation. Additionally, a linear bearing coupled to the support bed is slidingly movable along the elongated rail. Preferably, two such rails and correspondingly associated linear bearings insure that the support bed is urged reciprocatingly along a straight or axial pathway. In an embodiment of the invention where the frictional environment to be simulated constitutes the interior of an internal combustion engine, the first wear element is a portion of a cylinder wall, and a second wear element, as previously stated is a portion of a piston ring of an internal combustion engine.
The rotatory coupler, in a practical embodiment of the invention, constitutes a crank arrangement that has first and second crank portions radially displaced from one another. The reciprocating drive arrangement is coupled to the first crank portion, and the dynamic counterbalance arrangement is coupled to the second crank portion. As will be described herein, this crank arrangement permits the dynamic counterbalance arrangement to travel counter-reciprocatingly to achieve the desired balancing out of the second harmonic mechanical energy. Residual unbalance of the crank arrangement is corrected by the use of one or more balancing weights coupled thereto.
The dynamic counterbalance arrangement constitutes, in a highly advantageous embodiment of the invention, a counterweight that is urged in response to the reciprocating drive arrangement to travel reciprocatingly along a further substantially axial path of reciprocation. Preferably, this path is parallel to the substantially axial path of reciprocation of the support bed. In a preferred embodiment, two such counterweights are used in parallel. Each counterweight is provided with a guideway that constrains same to travel along respective substantially axial paths of reciprocation. The reciprocating travel by the reciprocating drive arrangement along the substantially axial path of reciprocation, and the reciprocating travel of the counterweight along the further substantially axial path of reciprocation, are out of phase with one another, and preferably 180xc2x0 out of phase. Thus, the relative motion is counter-reciprocatory. With respect to the linear drive that urges the second wear element toward the first wear element, there is provided a linear actuator that produces a linear force in a predetermined direction. Additionally, a cantilever arrangement delivers the linear force to the second support arrangement. In a preferred embodiment, the linear actuator is a pneumatic cylinder/piston assembly. An air regulator, which in some embodiments may be responsive to a CPU, controls the magnitude of the linear force applied by the pneumatic cylinder/piston assembly. A pivot coupling is provided for the cantilever member whereby the linear force is delivered to the second support arrangement in the direction that is opposite to the predetermined direction of linear force provided by the cylinder/piston assembly. A compression element couples the lever member to the second support arrangement. The force gauge, which may be a piezoelectric strain gauge is coupled to the compression member.
There is additionally provided a lubrication arrangement for delivering a lubricant to the first and second wear elements. The lubrication arrangement includes a pump for pumping the lubricant, and a nozzle for delivering the pumped lubricant to a predetermined location in relation to the first and second wear elements. A lubricant metering arrangement controls the rate of delivery of the lubricant to a predetermined flow rate. Illustratively, the flow rate is approximately between 0.2 xcexcl per h and 500 ml/h.
Temperatures controlled by a temperature control arrangement that may include a heater for delivering heat to the frictional wear interface, and a temperature monitoring arrangement, such as a thermal couple. In an embodiment of the invention that endeavors to simulate the internal characteristics of an internal combustion engine, the temperature is controlled to a range of approximately between 400xc2x0 C. and 600xc2x0 C.
In accordance with a further apparatus aspect of the invention, there is provided a system for collecting correlatable data responsive to a simulated friction environment between a cylinder wall wear element and a piston ring wear element, that are in frictional communication with one another. In accordance with the invention, there is provided a first support arrangement for supporting the cylinder wall wear element, and a reciprocating drive arrangement that drives the first support arrangement reciprocatingly along a substantially axial path of reciprocation. As previously indicated, a dynamic counter-reciprocating arrangement is coupled to the reciprocating drive arrangement for controlling the second harmonic inertial forces. A crank is coupled to the reciprocating drive arrangement and to the dynamic counter-reciprocating arrangement. A rotatory drive is coupled to the crank for supplying a rotatory mechanical energy thereto. A second support arrangement supports the piston ring wear element, and a linear drive is coupled to a second support arrangement for urging same in a direction that is transverse to the substantially axial path of reciprocation. The force is measured by a force gauge that is coupled to the linear drive for producing an electrical force signal that is responsive to the force applied by the linear drive to the second support arrangement. Lubrication is provided by a lubricant supply arrangement that delivers a lubricant to a predetermined side of the piston ring wear element. A rotational encoder produces an electrical rotatory data signal that contains rotatory information relating to a rotational position of the crank coupling arrangement.
In one embodiment of this further apparatus aspect of the invention, there is provided a data correlation arrangement for correlating the electrical force signal against the rotatory information in the electrical rotatory data signal. The rate of delivery of the lubricant is controlled by a lubricant supply flow rate controller which controls the flow rate to a predetermined flow rate within a range of approximately between 0.2 xcexcl/h and 500 ml/h. A controllable lubricant drain controls accumulation of the lubricant.
As previously noted, temperature is controlled by a temperature control arrangement that includes a thermocouple that is thermally in communication with the piston ring wear element. The linear actuator includes a pneumatic cylinder/piston assembly that receives regulated air for controlling the linear force applied by the pneumatic cylinder/piston assembly.
Variations in system speed are reduced by the use of a rotatory inertial mass coupled to the crank. As previously indicated, the rotatory inertial mass may be a pulley.
In an advantageous embodiment of the invention, the second support arrangement includes a two-point load transfer arrangement coupled to the piston ring wear element for enabling a frictional communication between the piston ring wear element and the cylinder wall wear element to be responsive to a resilience characteristic of the piston ring wear element. Circumferential and tilt displacements of the piston ring wear element with respect to the cylinder wall wear element are enabled in certain embodiments of the invention.
In accordance with a first method aspect of the invention, there is provided a method of collecting correlatable data responsive to a simulated friction environment between first and second wear elements in frictional communication with one another. The method includes the steps of:
first driving the first wear element along a predetermined path of reciprocation;
second driving a dynamic counter-reciprocating arrangement;
supporting the second wear element;
third driving the second support arrangement in a direction transverse to the predetermined path of reciprocation;
first producing an electrical force data signal responsive to a force applied the second wear element to the first wear element in response to the step of third driving; and
second producing an electrical rotatory data signal containing position information in response to the step of first driving.
In one embodiment of this method aspect of the invention, there are provided the further steps of:
calculating an instantaneous coefficient of friction for the frictional communication between first and second wear elements; and
correlating the instantaneous coefficient of friction to the electrical rotatory data signal.
In a further embodiment, the step of calculating an instantaneous coefficient of friction includes the further steps of:
first determining a friction force of the simulated friction environment between the first and second wear elements; and
calculating a ratio of the friction force of the simulated friction environment and the data in the electrical force data signal.
In a further embodiment, there is provided the further step of repeating the steps of calculating and correlating at each of a plurality of respective rates at which the step of first driving is performed.
In a further embodiment, there is provided the step delivering a predetermined quantity of lubricant to the region of frictional communication between the first and second wear elements. There is additionally provided the step of repeating the steps of calculating an correlating at each of the plurality of respective predetermined quantities of lubricants during the step of first driving. Thus, a friction environment can be created for various lubrication regimes.
In a further embodiment, there is provided the step of timing the electrical rotatory data signal for producing a speed signal.
In accordance with a further method aspect of the invention, there is provided a method of collecting correlatable data responsive to a simulated friction environment between first second and second wear elements in frictional communication with one another in accordance with the invention, the method includes the steps of:
first driving the first wear element along a predetermined path of reciprocation;
second driving a dynamic counter-reciprocating arrangement;
supporting the second wear element in a predetermined spatial relation to the first wear element;
third driving the second support arrangement in a direction transverse to the predetermined path of reciprocation; and
measuring a roughness characteristic of at least a selected one of the first and second wear elements.
In one embodiment of this further method aspect of the invention, the step of measuring includes the step of forming an optical photo-microscopic evaluation of the selected one of the first and second wear elements. The optical photo-microscopic evaluation contains information relating to distribution of the roughness characteristic over a predetermined surface area of the selected one of the first and second wear elements. In a further embodiment, the step of measuring includes the step of correlating a roughness characteristic of the selected one of first and second wear elements to a distance there along.